In order for a printing system (e.g. inkjet, electrophotographic, thermal, etc.) to print high quality images on a recording medium it is important to know what kind of media is about to be printed. In the case of inkjet, for example, preferred recording conditions differ for different type of media, partly because different media interact differently with ink. For instance, ink is able to wick along the paper fibers in plain paper, so that the spot of ink on the paper is enlarged and irregularly shaped relative to the drop of ink that strikes the paper. Media, which are specially formulated for high quality images, such as photographs, typically have one or more ink-receiving layers that absorb the ink in a more controllable fashion, so that the spot size and shape are more regular. Because the colorants are trapped closer to the media surface, and because a larger quantity of ink can be printed, (the associated carrier fluids being absorbed), an image printed on photographic print media has more vibrant colors than the same image printed on plain paper.
The appropriate amount of ink to use for printing an image on one type of media is different than printing on another type of media. If plain paper receives the same quantity of ink, more appropriately deposited in order to print a high-density image such as a photo that would be used for that same image on photographic print media, the plain paper may not be able to dry quickly enough. Even worse, the plain paper may cockle or buckle in the presence of excess ink, so that the printhead crashes into the printed image, thus smearing the image, and also possibly damaging the printhead. Even for two different types or grades of photographic print media, the amount of ink or number of passes to lay down an image for good tradeoffs in printing quality and printing throughput will be different. It is, therefore, important when receiving image-related data on a specific image to be printed, that the specific image be rendered appropriately for a specific media type that the image will be printed on. Image rendering is defined herein as determining data corresponding to: a) the appropriate amount of ink to deposit at particular pixel locations of the image, b) the number of overlapping passes needed to lay the ink down on the media in light of ink-to-ink and ink-to-media interactions, and c) the type of pattern needed to produce the image. In other words, an appropriate print mode is selected according to the media type, and the image is rendered according to that print mode.
Various means are known in the art for providing information to the printer or to an associated host computer regarding the type of media (e.g. glossy media of various grades, matte media of various grades, or plain paper) that is in the input tray of the printer. For example, the user may enter information on media type. Alternatively, there can be a barcode or other type of code pattern printed on the backside of the media that is read by the printer to provide information on media type as a sheet of media is picked from the input tray and fed toward the printing mechanism. Alternatively, media characteristics such as optical reflectance can be used to distinguish among media types. Generally, the processes for automatic media type detection require several seconds to provide accurate media-related information on media type. For competitive printers today, it is important to achieve excellent print quality at fast printing throughput. In particular, a user may be dissatisfied if the time required to print the first page of a print job is excessive.
U.S. Pat. No. 6,830,398 discloses one method providing faster printing throughput while enabling automatic media type detection prior to controlling conditions in the printing operation. In U.S. Pat. No. 6,830,398, a load detector is provided for detecting that recording media has been loaded into the printer. In addition, there is provided a sensor, such as a reflective optical sensor, that can discriminate the type of media type after the media has been loaded in the input but before paper feeding starts. In U.S. Pat. No. 6,830,398, when the printer is turned on, or after media loading has been detected, the sensor obtains information about the media type, even before the first page of media is picked for feeding to print a print job. However, conventional printers do not have a sensor capable of reliably discriminating paper type as described in U.S. Pat. No. 6,830,398. For example, the sensor in U.S. Pat. No. 6,830,398 would have difficulty discriminating between matte paper versus plain paper. To date, it has been found that improved reliability of media type detection is provided when the sensor (such as an optical reflective sensor) provides information regarding a plurality of regions of the recording medium.
U.S. Pat. No. 7,120,272 includes a sensor that makes sequential spatial measurements of a recording medium moving relatively to the sensor, where the recording medium contains repeated indicia to determine a repeat frequency and repeat distance of the indicia. The repeat distance is then compared against known values in a look-up table, for example, to determine the type of recording medium present.
In a carriage printer, such as an inkjet carriage printer, a printhead is mounted in a carriage that is moved back and forth across the region of printing. To print an image on a sheet of paper or other recording medium (also interchangeably referred to as paper or media herein), the recording medium is advanced a given distance along a recording medium advance direction and then stopped. While the recording medium is stopped and supported on a platen in a print zone relative to the printhead carriage, the printhead carriage is moved in a direction that is substantially perpendicular to the recording medium advance direction as marks are controllably made by marking elements on the recording medium, for example, by ejecting drops from an inkjet printhead. After the carriage has printed a swath of the image while traversing the recording medium, the recording medium is advanced, the carriage direction of motion is reversed, and the image is formed swath by swath.
U.S. patent application Ser. Nos. 12/037,970 and 12/250,717, disclose methods for identifying a general type of recording medium (e.g. photo paper versus plain paper) by analyzing a signal from a photosensor that is mounted on the printhead carriage. However, these co-pending patent applications disclose waiting until the recording medium is advanced into the print zone to scan the recording medium with the photosensor. This can increase the time required before the first print is available.
U.S. patent application Ser. No. 12/047,359, incorporated herein by reference in its entirety, discloses a method for identifying a type of recording medium by using identification marks provided on the recording medium, for example on its backside. An embodiment described therein uses the motion of the recording medium as it is being picked from the media input tray in order to move the identification marks past a sensor. In other words, U.S. patent application Ser. No. 12/047,359 discloses waiting until a print job is initiated and recording medium is being picked. This can increase the time required before the first print is available. Special methods for identifying locations of marks are also disclosed in U.S. patent application Ser. No. 12/047,359, in order to compensate for errors in measuring the spacing between marks that are due, for example, to media slippage during advance of the recording medium.
Commonly assigned co-pending U.S. patent application Ser. No. 12/332,670, discloses using an optoelectronic device mounted on the carriage to view a plurality of regions of the media input location as the carriage is moved, and to identify the media type while the media is still in the input location for the media. However, this requires an unobstructed optical path between the optoelectronic device on the carriage and the media input location, and such an unobstructed optical path is not available in all printing systems.
What is needed is a way to reliably identify a type of recording medium at a media input location in a printing system before a print job is initiated.